Copper is often used as interconnection material in integrated circuits. When forming a metal wiring of a semiconductor device, a thin film of copper (Cu) can improve the reliability of the semiconductor device as compared to using aluminum (Al). Copper has a higher melting point than aluminum and can improve the speed of signal transfer since it has a low specific resistance.
However, the etching characteristics of copper are very poor. Accordingly, a dual damascene process has been applied when using copper.